1. Field of the Invention
The present invention relates to the field of electronic control circuits for microelectronic measuring devices. Specifically, the invention relates to software-driven microcontroller and electronic circuits for monitoring and controlling quartz crystal microbalance (QCM) sensors, which are highly accurate devices for detecting minute quantities of mass deposited on the face of a crystal.
2. Description of the Related Art
QCM systems have been used for over two decades to measure minute quantities of mass. The principal components of a QCM system include a QCM sensor, an oscillator and control circuitry. In a QCM sensor there are typically two carefully matched quartz crystals aligned parallel to each other and separated by a small gap. Only one of the crystals, however, is exposed to the outside environment. The difference in frequency between the two crystals is the beat frequency, which is a very sensitive indication of the mass being deposited on the exposed crystal surface. The beat frequency is proportional to the mass of contamination that has accumulated on the sensing area and is electronically recorded in a digital electronic counter. Because QCM systems can measure very small amounts of mass deposited, they are often used when precise control over a system or process is desired or to monitor an environment.
QCM sensors have been used in spacecraft, for example, to measure film deposition on sensitive surfaces such as optical mirrors, thermal radiators and solar arrays. They have also been used in gas detection systems to measure contaminant concentrations in an ambient or closed environment. Still other QCM sensors have been used in semiconductor processing to precisely control chemical deposition in vacuum chambers and to monitor clean room contamination.
Control circuits associated with QCM sensors have been used almost as long as QCMs have existed. Conventional controls include an assembly of circuitry and sensors which may or may not consist of a QCM sensor signal conditioner, a QCM sensor temperature monitor, a thermal-electric heat pump controller and a microcontroller for data acquisition and data formatting. These elements have been collectively referred to as QCM controllers, controllers, or control circuits.
Requirements for control circuits are as varied as the applications for the QCM sensor. For example, QCM sensors that are moved in and out of a liquid environment have been fitted with controllers adapted to measure the sensor""s resonant frequency over a wide range of impedance. Other QCM sensors that are used to measure the mass of a substantial drop of liquid or particulate matter have been designed to correct for significant viscous damping losses. Still other QCM sensors that are used to monitor chemical environments have been constructed with control circuits that trigger an alarm and warning system. These controllers are typically constructed in large housing units with control panels and readout devices that impose significant weight and power resource requirements. As in most applications, the QCM sensor and controller are accessible; therefore, self-monitoring and wireless telemetry are not needed. Further, present controllers merely control the QCM sensor temperature. Additionally, conventional systems generally require a user to upload commands off-line or directly into the controller from a key-pad on the face of the controller box or from a key-board connected to a computer that is connected to the controller.
As QCM systems have found their way into spacecraft, missiles, and chemical applications, the need for small, lightweight, reliable, cost-effective, remotely-accessible systems capable of operation in extreme low temperatures has been observed. Further, in addition to determining mass, it is highly desirable to determine the electronic charge of particles and the molecular species of the material deposited on the QCM sensor""s quartz crystal. Current QCM systems do not include these desirable features.
It is an object of the invention to provide for the monitoring and control of a microelectronic sensor system.
It is a further object of the invention to provide an apparatus that self-monitors the health of one or more QCM sensors using a microcontroller with computer program instructions capable of controlling the QCM sensor temperature and monitoring the QCM temperature, beat frequency and controller operations, among other things.
It is another object of the invention to provide for a communications system using data telemetry and uplink circuits that allow a remote user to retrieve processed data and to send commands as needed to ensure proper operation of the QCM sensor system or allow the software-driven microcontroller to make adjustments.
It is still another object of the invention to provide for extended operations without taxing finite weight, energy and cost limits such as those imposed in space flight operations.
It is still another object of the invention to operate at extreme cold temperatures, such as those experienced in outer space.
It is still another object of the invention to capture electronic signals including, but not limited to QCM beat frequency, duty cycle, and amplitude and QCM sensor and controller temperature current, convert the signals to data records and then report the data quickly to a remote user to enhance the system""s capability and reliability over conventional systems.
It is still another object of the invention to provide a controller using innovative nano-connectors and miniature wiring to achieve a 100-fold reduction in size compared to conventional controllers thereby making the present invention portable and easy to incorporate into existing facilities that have limited space. This also provides for reduced construction and operating costs.
It is still another object of the invention to be assembled in modular units thereby being highly flexible.
It is a further object of the present invention to provide a controller that is modifiable by a user so that it can be reconfigurable during operation.
These and other objects of the invention are described in the description, claims and accompanying drawings and are accomplished by a controller, for controlling an apparatus including a microelectronic sensor and for conditioning electronic signals having associated therewith electronic circuits and self-monitoring software. The controller includes a controller thermal monitor for detecting a temperature of the apparatus and outputting a controller temperature signal, a first temperature measuring circuit for detecting the controller temperature signal from the controller thermal monitor, a second temperature measuring circuit for detecting a temperature signal from the microelectronic sensor and outputting a current signal, a signal conditioning circuit for receiving and conditioning a beat frequency signal from the microelectronic circuit, a microcontroller, connected to the controller thermal monitor, the first and second temperature measuring circuits, and the signal conditioning circuit, for converting the controller temperature signal, the microelectronic sensor temperature signal, the current signal, an amplitude of the beat frequency signal, a voltage from the microelectronic sensor, and the beat frequency signal into data records and for manipulating the data records for transmission. The controller can also include a thermal-electric heat pump circuit, connected to the microelectronic sensor and the second temperature sensing circuit, for detecting the temperature signal from the second temperature sensing circuit and outputting an electric current and for heating and cooling the microelectronic sensor by switching the direction of the electric current, and a power switch for energizing the microelectronic sensor.
The present invention also includes an apparatus for controlling a microelectronic sensor and conditioning electronic signals having associated therewith electronic circuits and self-monitoring software, including a sensor circuit, for precisely detecting temperature and minute changes in mass deposition and outputting a temperature signal associated with a temperature and outputting a beat frequency signal proportional to said mass deposition and a controller circuit for monitoring the health of the sensor means and conditioning the beat frequency signal. The controller circuit can include a controller thermal monitor for detecting a temperature of the controller circuit and outputting a controller temperature signal, a first temperature measuring circuit for measuring the controller temperature signal from the controller thermal monitor, a second temperature measuring circuit for detecting the temperature signal from the sensor circuit, a thermal-electric heat pump circuit for receiving an electric current and for raising or lowering the temperature of the sensor circuit by switching direction of the electric current to the thermal-electric heat pump and for turning off the heat pump, a signal conditioning circuit for receiving and conditioning the beat frequency signal from the sensor circuit and a microcontroller, connected to the controller thermal monitor, the first and second temperature measuring circuits, the thermal-electric heat pump circuit, and the signal conditioning circuit, for converting the controller temperature signal, the sensor circuit temperature signal, the second temperature measuring circuit current, beat frequency and amplitude, microelectronic sensor voltage, and the beat frequency signal into data records and for manipulating said data records for transmission.
The sensor circuit can be any QCM.
The controller circuit can further include a remote user for providing commands remotely, a power switch for energizing power to the sensor circuit, an uplink circuit for receiving commands from the remote user and a telemetry circuit for capturing data records and transmitting data records to the remote user.
The thermal monitor can be a platinum resistive temperature device, a thermocouple, or other thermal monitor device.
The sensor circuit can further include a high voltage grid for attracting specific charged particles for mass measurement by switching a polarity of the high voltage grid to either positive or negative with reference to ground and an insulator for insulating the sensor circuit from the electric current from the high voltage grid and the sensor circuit.
The apparatus may be part of a system that is used in a chemical deposition process, space flight operations, to monitor for chemical contamination in an enclosed or ambient air environment, and/or for biological detection.
The apparatus may include a computerized method for controlling a QCM sensor, the method includes the steps of initializing system variables and establishing default and set-point values; energizing a potential across QCM sensor system terminals, thereby energizing QCM sensor quartz crystals, a thermal-electric heat pump, and a high voltage grid contained within the QCM sensor; detecting the voltage signal amplitude and voltage signal frequency of the QCM sensor system quartz crystals, the voltage amplitude of the QCM sensor system thermal monitor, and the current of the controller thermal monitor and QCM sensor power supply, and producing individual signals representative thereof; amplifying the quartz crystal voltage amplitude signal and calculating the duty cycle and waveform thereof, supplying the previous signals and the calculated duty cycle and waveform calculated above to a microcontroller for conversion into data records; comparing the data records to the default or set-point values; adding synchronization codes to the data records; transmitting the data records through a wired or wireless communications system to a remote computer or computer network; receiving incoming commands from the remote computer or computer network; and adjusting the voltage supply to the thermal-electric heat pump as a result of the incoming commands of the deviation from the default or set-point values. Moreover, the method may also include the steps of slowly heating the QCM sensor quartz crystals and detecting the voltage signal amplitude and voltage signal frequency of vibration of the QCM sensor system quartz crystals over time; calculating a sublimation and evaporation temperature corresponding to the material deposited on the QCM quartz crystal; and supplying the voltage signal amplitude and voltage signal frequency associated with the QCM sensor system quartz crystals and the sublimation and evaporation temperature corresponding to the material deposited to the microcontroller for conversion into data records.